8 BULLETIN 739, U. S. DEPARTMENT OE AGRICULTURE. 
It is not difficult to explain the presence of bacteria of the aerogenes 
type in air either inside or outside the barn, for they appear to be 
widely distributed on grains and other feeds, and in the soil. Rogers, 
Clark, and Evans (15) in their study of 166 organisms of the col on- 
aerogenes group occurring on grains, found that 151 were of the B. 
aerogenes type, while 8 resembled but were not identical with the B. 
coli type. An examination of many samples of alfalfa, cane, corn, 
and kafir-corn forage by Hunter (5) at the time of filling the silo 
showed coZi-like cultures ranging in number from 1,000 to 1,000,000 
per gram. A study of 95 of the organisms isolated from different 
kinds of silage, and of 15 strains obtained from growing fields of alfalfa 
and kafir corn showed about 21 per cent to be of the B. coli type and 
79 per cent of the B. aerogenes type, as differentiated by the methyl- 
red test. 
That coZi-like organisms are present in soil has been shown by 
Johnson and Levine (7), who found them more prevalent in soils upon 
which crops were growing than in absolutely fallow areas receiving 
soil treatment. Aerogenes-cloacge types were found to be the pre- 
dominant coZi-like forms in the soil. 
It is apparent that the B. aerogenes type found in air may be 
derived from various sources, and it is not inconceivable that the 
organisms of this type found in market milk produced under clean 
conditions are the descendants of those introduced into the fresh milk 
in extremely small numbers by means of air contamination. It is also 
possible to contaminate milk with organisms of the B. aerogenes type 
by using unsterilized utensils. 
Having surveyed the various means by which fresh milk is infected 
with organisms of the colon-aerogenes group it is now possible to 
answer the question "T>o organisms of the colon-aerogenes group 
indicate the presence of manure in fresh milk ? ? ' The presence of the 
B. coli type indicates manurial contamination either directly from 
fecal material which drops into the milk principally from the body 
of the cow or indirectly through unsterilized utensils. It must be 
pointed out that the contamination by cow feces represents a much 
more serious form than that from unsterilized utensils. This state- 
ment may be explained by the fact that the introduction of cow feces 
into milk may carry organisms of bovine tuberculosis. Schroeder (19) 
has shown that cattle having tuberculosis swallow their sputum, and 
the tubercle bacilli in it pass through their bodies and out into the 
feces. The contamination of milk through unsterilized utensils 
represents a condition of careless handling in which there has been 
growth of the B. coli type in the utensils. While this kind of con- 
tamination may add as large a number of the B. coli type to milk as 
the fecal, it would not represent the same possibilities for infection 
with the bovine tubercle bacillus as does the latter. So far as the 
